Practical and technical aspects for the 3D scanning of lithic artefacts using micro-computed tomography techniques and laser light scanners for subsequent geometric morphometric analysis. Introducing the StyroStone protocol

Here, we present a new method to scan a large number of lithic artefacts using three-dimensional scanning technology. Despite the rising use of high-resolution 3D surface scanners in archaeological sciences, no virtual studies have focused on the 3D digitization and analysis of small lithic implements such as bladelets, microblades, and microflakes. This is mostly due to difficulties in creating reliable 3D meshes of these artefacts resulting from several inherent features (i.e., size, translucency, and acute edge angles), which compromise the efficiency of structured light or laser scanners and photogrammetry. Our new protocol StyroStone addresses this problem by proposing a step-by-step procedure relying on the use of micro-computed tomographic technology, which is able to capture the 3D shape of small lithic implements in high detail. We tested a system that enables us to scan hundreds of artefacts together at once within a single scanning session lasting a few hours. As also bigger lithic artefacts (i.e., blades) are present in our sample, this protocol is complemented by a short guide on how to effectively scan such artefacts using a structured light scanner (Artec Space Spider). Furthermore, we estimate the accuracy of our scanning protocol using principal component analysis of 3D Procrustes shape coordinates on a sample of meshes of bladelets obtained with both micro-computed tomography and another scanning device (i.e., Artec Micro). A comprehensive review on the use of 3D geometric morphometrics in lithic analysis and other computer-based approaches is provided in the introductory chapter to show the advantages of improving 3D scanning protocols and increasing the digitization of our prehistoric human heritage.

This protocol presents the first detailed step-by-step pipeline for the 3D scanning and post processing of large batches of lithic artefacts using a micro-computed tomography (micro-CT) scanner (i.e., a Phoenix v-tome-x S model by General Electronics MCC, Boston MA) and an Artec Space Spider scanner (Artec Inc., Luxembourg). This protocol was used to scan more than 700 lithic artefacts from the Protoaurignacian layers at Fumane Cave in north-eastern Italy (https://doi.org/10.5281/zenodo.6362150).
For this study several costly scanners and proprietary software packages were employed. Although it is not easy to find a low-budget alternative for the scanners, it is possible to use free and open-source software programs, such as 3D-Slicer (https://www.slicer.org/) or MorphoDig (https://morphomuseum.com/morphodig), to process CT data as well as MeshLab (Cignoni et al. 2008) to interact with the 3D models in general. However, if alternative software is used, the steps and their order described in this protocol might diverge significantly.
A cost-effective alternative to create 3D models is digital photogrammetry using commercial cameras and freely available software like Meshroom (https://alicevision.org). Although photogrammetry is an affordable technique to create accurate 3D models of objects, this method might not be useful when scanning large batches of artefacts, as it will require a lot of computation time and processing capacity. Likewise, it could be difficult to generate accurate 3D models of very small and/or detailed tool shapes using 3D surface scanners because stone tools are often much smaller than the recommended minimum field of view. Similarly, the resolution of conventional medical CT scanners might not be sufficient to capture minor details of stone tools, such as the outline or dorsal scars.
This protocol aims at providing the first detailed procedure dedicated to the scanning of small lithic implements for further three-dimensional analysis. Note that some of the steps must be repeated at different working stages throughout this protocol. In cases where a task must be done in the exact same way as described in a previous step, a reference to that step is provided. When slight changes were made, the step was modified and reported entirely. This micro-CT scanning: micro-CT scanning: A micro-CT scanner Associated scanning software (e.g., Phoenix Datos-X software; General Electronics MCC).
A workstation powerful enough to process large 3D datasets -Used here: - 2 Identify the scanning size limitations of the micro-CT scanner.
3 Cut the Styrofoam body into a rectangle according to the dimensions determined in Step 2.
3.2 Glue the two Styrofoam pieces together with Polyvinyl acetate (white glue). 4 Draw guiding or separation lines with a dark marker on both sides (Face A and B) of the Styrofoam body depending on the size and number of artefacts that need to be scanned -these will determine the rows or lines in which the artefacts will be placed one after another.
The row separation will help to keep the artefacts in the same orientation and will simplify the subsequent 3D model extraction after the CT-scanning process.
5 Draw a mark (e.g., a dot or "A") on the first side of the Styrofoam (Face A), which will later facilitate the correct identification of the artefacts. 6 Carve holes along rows into the Styrofoam with a box cutter that are roughly the same dimensions of the artefacts. They should be secure enough to ensure a stable positioning and protect the artefacts from moving during the CT-scanning process.
6.1 Insert the artefact directly into its hole and immediately document its position in the Styrofoam as described in Step 6.2 Step 6.2 (Fig. 1).
On Face A, place the first artefact on the left most position of the first row and continue in this line towards the right until the line is fully occupied. Then continue with the second row below, again starting at the left side until Face A is completed. Continue with Face B in the same way.
Insert lithics following the best-suited criteria depending on how the lithic assemblages are curated (e.g., stratigraphic units, raw materials, ID numbers) or according to the size variation of the artefacts if necessary.
Always use the same orientation of the artefacts, i.e., dorsal face facing upwards and proximal side at the bottom. By placing the longest axis of the specimen vertically, the object thickness between the source and the detector remains limited during the scanning process, requiring less x-ray penetration power and thus reducing energy costs. Moreover, during the later post-processing step, such an orientation will enable easier identification and virtual separation among 3D scans of lithics when compared with the reference list of artefacts (Step 6.2 Step 6.2) and reference photographs of the Styrofoam body (Step 7.1 and 7.2 Step 7.1 and 7.2).  6.2 Document the exact position of each artefact in a spreadsheet (e.g., MS Excel) directly after it is inserted into its Styrofoam hole.
Clearly indicate the Styrofoam side, row, and at which numeric position the artefacts are located. For simplicity reasons you might use a coded identification key.
Example: An artefact with the location code S1 S1-FA-L2.5 FA-L2.5 would be inserted into first Styrofoam body (S1 S1; only in cases where several bodies must be used to scan large amounts of lithics) Face A (FA FA, first Styrofoam side) in the second row from the top to the bottom (L2 L2) and at the fifth position from the left to the right (.5 .5) in this row.
Keeping track of the positions is extremely important and will not only ensure the fast and correct labelling of the right artefact ID with the 3D models, but also ensure the artefacts are safely returned to their find bags. Therefore, you might use a handwritten list as backup. This is an open access protocol distributed under the terms of the Creative Co mmo ns Attributio n License Creative Co mmo ns Attributio n License (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, 7.2 Take a picture of the first artefact of the first row of each face. This will serve as a reference to orient the 3D model of the entire face, making the later identification of the artefacts' order much easier. 8 Cover the Styrofoam faces with Styrofoam slabs. 8.1 Cover both Faces A and B with a thin Styrofoam slab (ca. 1 cm thickness) of the same dimensions as the main Styrofoam body (Step 3 Step 3).
8.2 Tightly secure the two Styrofoam slabs and main Styrofoam body with plastic rubber bands (Fig. 2). Do not glue them together, as it will be difficult to disassemble when removing the lithics after scanning.

Repeat
Step 1 to Step 8.2 Step 1 to Step 8.2 if more Styrofoam bodies are needed (S1, S2, etc.; see Step 6.2 Step 6.2 for labelling). 9.1 Label each Styrofoam body with a number to identify them afterwards (Fig. 3).  Note: CT-scanning is usually performed by a certified and trained technician using the scanning parameters specified below and depending on the inherent nature of the different raw materials. The following steps are a summary of the scanning process performed for our case study, which relied on the scanning of fine-grained chert bladelets with thicknesses between 0.5 mm to 6.0 mm (mean: 2.4 mm).
In our study, each scan took approximately 2:20 hours and we scanned up to 220 bladelets per scan (these bladelets had an average size of 28 x 8 x 2.4 mm).
Place the Styrofoam body on the turning base of the CT-scanner (Fig. 4).

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Citatio n: Citatio n: Dominik GÃ Â ¶ldner, Fotios Alexandros Karakostis, Armando Falcucci StyroStone: A protocol for scanning and extracting three-dimensional meshes of stone artefacts using Micro-CT scanners https://dx.doi.org/10.17504/protocols.io.4r3l24d9qg1y/v2 12 The turning base should be positioned as far as possible from the source to increase the field of view and, therefore, the number of lithics that can be scanned at one time. Note that with greater distance from the source, the resolution decreases.
13 Set up the machine according to the best scanning parameters -usually done by the scanning technician.
For scanning multiple specimens at the same time, it is advisable to use the "multiscans" option, which enables the device to scan longer targets within the same scanning session. In particular, using the scanner's associated computer device and software (e.g., Phoenix Datos-X software; General Electronics MCC), the scanning technician virtually separates the target into different layers (by Styrofoam height) to be scanned individually (per layer/scan), which are then automatically merged before model reconstruction. It must be highlighted that the use of this option might produce visual artefacts in the resulting 3D models, appearing as lines at the borders in between the layered scans (i.e., "merging lines"). To ensure that these lines will not affect stone tool morphology, the technician should make sure that the selected upper and lower borderlines of each layer/scan do not intersect any stone tools.
The resolution used across our scans was ca. 140 microns. Resolution largely depends on the distance 9 Citatio n: Citatio n: Dominik GÃ Â ¶ldner, Fotios Alexandros Karakostis, Armando Falcucci StyroStone: A protocol for scanning and extracting three-dimensional meshes of stone artefacts using Micro-CT scanners https://dx.doi.org/10.17504/protocols.io.4r3l24d9qg1y/v2 This is an open access protocol distributed under the terms of the Creative Co mmo ns Attributio n License Creative Co mmo ns Attributio n License (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, between the source and the target/object. Even though the utilized micro-CT scanner is technically capable of producing models with much greater resolution, our experiments showed that 140 microns was a good balance, allowing us to scan a large number of artefacts at once, while avoiding distinguishable inaccuracies in the resulting 3D surface form (size and shape) of the blades and bladelets.
14 Start scanning process.
15 After the scanning process is completed, save the scans onto a hard disk. Make sure to save the scanning metadata (e.g., as .pcr file), including all scanning parameters, which are required to open and scale the CT scans (e.g., in Avizo). Important scanning parameters to successfully load the CT data into Avizo Lite are the resolution (Voxel size), volume dimensions (x, y, z), and image data type (e.g., 16 bit).
16 Visualize the overall scanning result to check for obvious errors. This can be done by reconstructing the CT data and exporting the file as an image stack, e.g., as .tiff files or .vol files, which can be opened in Avizo Lite. Reconstruction of the CT data can be performed, visualized, and exported using software like Phoenix Datos-X.
17 Take the scanned Styrofoam body from the CT scanner.
18 Dismantle the Styrofoam body by taking off the plastic rubber strings and the covering plates.
19 Remove the artefacts one by one from the Styrofoam and put them back into their respective find bags.
Part 3 -3D model extraction of CT scanned stone artefacts using Avizo Part 3 -3D model extraction of CT scanned stone artefacts using Avizo 20 Note: Note: For our project the preparation and separation of the faces took around 2 hours per Styrofoam body. The subsequent extraction of each lithic described in the next chapter (Part/Section 4) only took around one minute per artefact.

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Citatio n: Citatio n: Dominik GÃ Â ¶ldner, Fotios Alexandros Karakostis, Armando Falcucci StyroStone: A protocol for scanning and extracting three-dimensional meshes of stone artefacts using Micro-CT scanners https://dx.doi.org/10.17504/protocols.io.4r3l24d9qg1y/v2 This is an open access protocol distributed under the terms of the Creative Co mmo ns Attributio n License Creative Co mmo ns Attributio n License (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, Open CT scan in Avizo Lite. This is an open access protocol distributed under the terms of the Creative Co mmo ns Attributio n License Creative Co mmo ns Attributio n License (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, This is an open access protocol distributed under the terms of the Creative Co mmo ns Attributio n License Creative Co mmo ns Attributio n License (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, This is an open access protocol distributed under the terms of the Creative Co mmo ns Attributio n License Creative Co mmo ns Attributio n License (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, 14 Citatio n: Citatio n: Dominik GÃ Â ¶ldner, Fotios Alexandros Karakostis, Armando Falcucci StyroStone: A protocol for scanning and extracting three-dimensional meshes of stone artefacts using Micro-CT scanners https://dx.doi.org/10.17504/protocols.io.4r3l24d9qg1y/v2 Note: Note: you should usually aim for the parameters 'Volume_Size[X, Y, or Z]' (blue arrow in Fig. 9), especially when the ROI (Region of Interest) was specified before the scanning process. In our case ROI was not specified and is therefore identical to the volume size. If ROI is specified by the technician, the ROI parameter reported in the metadata file will only show a part of the image. This is an open access protocol distributed under the terms of the Creative Co mmo ns Attributio n License Creative Co mmo ns Attributio n License (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, 20.9 Leave all other parameters in 'Raw Data Parameters' window as the pre-sets and press 'Okay'. 20.10 Indicate unit in 'Units Editor' window ( Fig. 10) according to indicated voxel size unit in pcr CT-scan metadata file ('VoxelSizeRec=NUMBER', yellow arrow in Fig. 9) and press 'Okay'.  21.2 Click on the newly generated 'Isosurface' label ( Fig. 12) and choose a 'Threshold' value (yellow arrow in Fig. 12) that separates the artefacts from the surrounding air, Styrofoam etc.
Enable and use 'Down Sample' (pink arrow in Fig. 12) to run a fast isosurface test extraction to check whether the chosen 'Threshold' value works well.
Time can be saved by finding a good threshold, as this lessens the need for cleaning and outlier removal. Note that a preview mode is not available, so it is not possible to judge whether the chosen 'Threshold' value works well overall. Therefore, it might be necessary to test multiple values before a good separation can be achieved (Step Step This is an open access protocol distributed under the terms of the Creative Co mmo ns Attributio n License Creative Co mmo ns Attributio n License (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, 21.5 21.5). It might be useful to note down the values that have already been tested and to narrow down a suitable Threshold value range. 21.4 When completed, inspect the resulting isosurface model (Fig. 13 and 14) and check for This is an open access protocol distributed under the terms of the Creative Co mmo ns Attributio n License Creative Co mmo ns Attributio n License (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, 'unusual' or 'unnatural' surface inconstancies, 'noise', and scanning artefacts.

If the chosen 'Threshold' value does not work well, repeat
Step 21.2 Step 21.2 and 21.3 21.3 until a good separation is be achieved. If the chosen threshold works well, continue with Step Step 21.6. 21.6.

If a suitable threshold value was found, repeat
Step 21.2 Step 21.2 and 21.3 21.3 using the indicated threshold value (e.g., by copy and paste) but this time with 'Down Sample' disabled. 21.7 When completed, again inspect the resulting isosurface model (Fig. 13 and 14) and check surface inconstancies (see Step 21.5 Step 21.5).

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Citatio n: Citatio n: Dominik GÃ Â ¶ldner, Fotios Alexandros Karakostis, Armando Falcucci StyroStone: A protocol for scanning and extracting three-dimensional meshes of stone artefacts using Micro-CT scanners https://dx.doi.org/10.17504/protocols.io.4r3l24d9qg1y/v2 This is an open access protocol distributed under the terms of the Creative Co mmo ns Attributio n License Creative Co mmo ns Attributio n License (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, 21.8 If the chosen 'Threshold' value does not work well, repeat Step 21.2) Step 21.2) and 21.3 21.3 until a good separation is achieved. 22 Remove remaining materials. 22.1 Select the 'Eye' sign in the top menu bar above the 3D viewing panel (grey arrow in Fig.   15) to switch to orthographic view ('Eye' sign with parallel sight lines).  Fig. 15).

Select the vol file label (yellow arrow in
22.3 Rotate the 3D model into a proper position (e.g., as shown in Fig. 15) that allows for easier removal of the unnecessary outlying material. Fig.   15). Fig. 15).

Select the first 'Tool' sign (Cropping tool) in the options bar (pink arrow in
Use the left mouse button and cursor to narrow the bounding box (brown arrows in Fig.   20 Citatio n: Citatio n: Dominik GÃ Â ¶ldner, Fotios Alexandros Karakostis, Armando Falcucci StyroStone: A protocol for scanning and extracting three-dimensional meshes of stone artefacts using Micro-CT scanners https://dx.doi.org/10.17504/protocols.io.4r3l24d9qg1y/v2 This is an open access protocol distributed under the terms of the Creative Co mmo ns Attributio n License Creative Co mmo ns Attributio n License (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, 22.6 15). If possible, leave only the lithic artefacts within the bounding box (Fig. 16). Any remaining materials can still be excluded later if necessary. Switch between 'Cursor' and 'Hand' (i.e., dragging) mode and change the position of the 3D model to adjust bounding box in all dimensions to crop out as much of the outlying material as possible. 23 Generate isosurface again for cropped scan. Fig. 17) that appears over the options bar to generate an isosurface of the scan (like Step 21.1

Click on vol file label and then on the 'Isosurface' button (blue arrow in
Step 21.1).

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Citatio n: Citatio n: Dominik GÃ Â ¶ldner, Fotios Alexandros Karakostis, Armando Falcucci StyroStone: A protocol for scanning and extracting three-dimensional meshes of stone artefacts using Micro-CT scanners https://dx.doi.org/10.17504/protocols.io.4r3l24d9qg1y/v2 This is an open access protocol distributed under the terms of the Creative Co mmo ns Attributio n License Creative Co mmo ns Attributio n License (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, 23.2 Click on the newly generated 'Ie,sosurface' label (yellow arrow in Fig. 18). Disable 'Down Sample' and insert the 'Threshold' value identified to be sufficient earlier in Step 21.2 Step 21.2 or Step 21.5 / 21.6 Step 21.5 / 21.6. fig. Fig. 18) and wait until the process has completed. 24 Extract surface from cropped isosurface.

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Citatio n: Citatio n: Dominik GÃ Â ¶ldner, Fotios Alexandros Karakostis, Armando Falcucci StyroStone: A protocol for scanning and extracting three-dimensional meshes of stone artefacts using Micro-CT scanners https://dx.doi.org/10.17504/protocols.io.4r3l24d9qg1y/v2 This is an open access protocol distributed under the terms of the Creative Co mmo ns Attributio n License Creative Co mmo ns Attributio n License (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, This is an open access protocol distributed under the terms of the Creative Co mmo ns Attributio n License Creative Co mmo ns Attributio n License (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, 26.11 Click 'Save' to save the labels.

Close Avizo Lite.
Part 4 -Cropping extracted surface model to separate Face A and B in Artec Studio Part 4 -Cropping extracted surface model to separate Face A and B in Artec Studio 27 Load 3D model into Artec (Fig. 22). 27.8 Inspect loaded model in Artec Studio (Fig. 23). This is an open access protocol distributed under the terms of the Creative Co mmo ns Attributio n License Creative Co mmo ns Attributio n License (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, 28.5 Press and hold Ctrl while pressing and moving the left cursor over the material from Face B. Selected areas will be highlighted in red (Fig. 24).
28.6 Click 'Erase' in the Eraser Panel or press the 'Delete' key to delete the selected area ( Fig. 25).
29.2 To remove the outlying materials, press and hold Ctrl while pressing and dragging the left cursor over the materials. Selected areas will be marked in red (Fig. 26). Step 29.2 until only the stone artefacts remain. It might help to rotate the entire scan to get a better viewpoint.
30 Save the isolated and cleaned Face (Fig. 27). This is an open access protocol distributed under the terms of the Creative Co mmo ns Attributio n License Creative Co mmo ns Attributio n License (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, 30.6 In the storage folder duplicate Face A file by copying it to create a backup file. Name it accordingly (e.g., "Styro 1_Face A_Cropped and Cleaned_Backup"). 31 Repeat the workflow for Face B with the copied version of the extracted Avizo file from Step 27.1.
Step 27.1. Remember to position the scan so that their order corresponds to their actual order, i.e., the first artefact in the model must be the first on in the list, so it is placed on the upper left. Also remember to look at the scan from the correct side. The scan can also be oriented using the reference pictures. Selected areas will be marked in red (Fig. 28).

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Citatio n: Citatio n: Dominik GÃ Â ¶ldner, Fotios Alexandros Karakostis, Armando Falcucci StyroStone: A protocol for scanning and extracting three-dimensional meshes of stone artefacts using Micro-CT scanners https://dx.doi.org/10.17504/protocols.io.4r3l24d9qg1y/v2 This is an open access protocol distributed under the terms of the Creative Co mmo ns Attributio n License Creative Co mmo ns Attributio n License (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, 34.6 Click 'Erase' in the Eraser Panel or press the 'Delete' key to delete the selected rows. 34.7 Alternatively, you can select the line that you want to separate and then inverse the selection with the 'Inverse' button in the Eraser Panel. To delete the selection, apply Step 34.6 Step 34.6. 35 Save the separated line (Fig. 29). 30. Remember to position the scan so that the artefacts in the model correspond to their actual order, i.e., the first artefact in the model must be the first on in the list, so it is positioned in the upper left. Also remember to look at the scan from the correct side. This can be done by orienting the scan using the reference pictures.   43.5 Press and hold Ctrl while selecting all artefacts but the one that you want to separate. Selected artefacts will be highlighted red (Fig. 31). 43.6 Click 'Erase' in the Eraser Panel or press the 'Delete' key to delete the selected artefacts. 43.7 Alternatively, you can also select only the artefact that you want to separate and then inverse the selection with the 'Inverse' button in the Eraser Panel. To delete the selection, apply Step 43.6 Step 43.6.
Export and save the separated artefact (Fig. 32).

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Citatio n: Citatio n: Dominik GÃ Â ¶ldner, Fotios Alexandros Karakostis, Armando Falcucci StyroStone: A protocol for scanning and extracting three-dimensional meshes of stone artefacts using Micro-CT scanners https://dx.doi.org/10.17504/protocols.io.4r3l24d9qg1y/v2 This is an open access protocol distributed under the terms of the Creative Co mmo ns Attributio n License Creative Co mmo ns Attributio n License (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, 44.2 Click on 'Export as'. 44.3 Navigate to the target folder. 44.4 Name the cropped artefact with the actual artefact ID. 44.5 It might also be useful to add information on the exact location within the Styrofoam scan to trace potential errors. A possible location ID which can be added either before or after the actual artefact ID in the file name could look like this: S1-FA-L1.1_10401 S1-FA-L1.1_10401

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Citatio n: Citatio n: Dominik GÃ Â ¶ldner, Fotios Alexandros Karakostis, Armando Falcucci StyroStone: A protocol for scanning and extracting three-dimensional meshes of stone artefacts using Micro-CT scanners https://dx.doi.org/10.17504/protocols.io.4r3l24d9qg1y/v2 This is an open access protocol distributed under the terms of the Creative Co mmo ns Attributio n License Creative Co mmo ns Attributio n License (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, If all artefacts are measured, errors in the database could also be cross-checked. However, with larger sample sizes, this may take a lot of time. Linear measurements (e.g., maximum length of the artefact) can easily be taken in MeshLab (Cignoni et al. 2008) then compared with physically measured variables in the main database. For any subsequent intra-or interobserver error and methodological evaluations, it might be useful to store the virtual control measurements in an extra column of the main database. To save time, this task can easily be combined with the export of the models to non-binary ply. files if necessary for subsequent analysis in the R package geomorph (see below).
Open MeshLab. 50 To load the first artefact into MeshLab, drag the model file and drop it into the 3D View Panel of MeshLab. Alternatively, click on 'File' in the top menu bar and choose 'Import Mesh', then navigate to the target folder and open the desired model by pressing 'Open' (Fig. 33). 52 Click on the 'Point to Point Measure Tool' in the Tool bar above the 3D View Panel (blue arrow in Fig.   33). In this mode, the tracking ball will vanish, making it impossible to rotate the model (but see note within Step 54 Step 54).
53 Click with the left mouse curser on the starting point of the measurement.